The present invention relates to a multi-test assembly for evaluating, detecting and monitoring processes at elevated pressure, and uses of the mufti-test assembly. Further, the present invention relates to a system for fast, systematic and effective testing and detection of solids formation such as those used for testing and optimizing of chemicals for controlling gas hydrates.
One of the most challenging problems in oil and gas exploration is the presence of natural gas hydrates in transport pipelines and equipment. Natural gas hydrate is an ice-like compound consisting of light hydrocarbon molecules encapsulated in an otherwise unstable water crystal structure. These hydrates form at high pressures and low temperatures wherever a suitable gas and free water are present. Gas hydrate crystals can become deposited on pipeline walls and in equipment, and in the worst case, lead to complete plugging of the system. Costly and time-consuming procedures may be needed to restore flow again. In addition to the economic consequences, there are also numerous hazards connected to hydrate formation and removal. Although gas hydrates are generally thought of as a problem mostly in connection with gas production, they are also a significant problem for condensate and oil production systems.
To control gas hydrates, the usual approach has been to take steps to avoid any hydrate formation at all. This can be achieved by keeping pressure low (often not possible from flow or operational considerations), keeping temperature high (usually by insulating), removing the water completely (costly equipment and difficult), or by adding chemicals that suppress hydrate formation thermodynamically or kinetically. Insulation is very often used, but is not sufficient alone. Adding chemicals, specifically methanol (MeOH) or ethylene glycol (EG), is therefore the most widespread hydrate control mechanism in the industry today (E. D. Sloan Jr., Clathrate Hydrates of Natural Gases, Marcel Dekker, Inc., New York, 1998, pp. 164-170). These antifreezes ,expand the pressure-temperature-area of safe operation, but are needed in large quantitiesxe2x80x9450% of the water liquid fraction is not unusual in water-rich production. The use of MeOH in the North Sea may approach 3 kg per 1000 Sm3 of gas extracted. The need for such large amounts of antifreeze places severe demands on logistics of transportation, storage and injection in offshore facilities with a deficiency of space.
Inhibitor chemicals of different types are not only used in pipeline transport and processing areas, but also extensively in drilling operations and wells.
Mainly due to the huge amounts and large costs involved in using traditional inhibitors like MeOH, there has ver the last decade been extensive efforts devoted to finding chemicals which may be effective at controlling hydrates at much lower concentrations.
Many oil companies and research institutes have contributed to this effort, and at present, the results are divided into three main categories; kinetic inhibitors, dispersants, and modificators. Kinetic inhibitors have: an affinity for the crystal surface, and thereby can be used to prevent hydrate crystal growth. Dispersants act as emulsifiers, dispersing water as small droplets in the hydrocarbon liquid phase. This limits the possibilities for hydrate particles to grow large or to accumulate. The modifiers act as a combination of the two other methods, attaching to the crystal surface, the hydrate is dispersed as small particles in the hydrocarbon liquid phase.
Dispersant and modifiers are generally dedicated for condensate and oil production systems.
The development of low dosage chemicals for hydrate control has been somewhat successful, although there are practical and environmental drawbacks to most of them.
One principal reason for the limited success has been the lack of a method and a system for fast systematic and effective testing of large test matrixes for new chemicals. Most of these chemicals work efficiently only in blends. Further, the blends have to be suited to each field fluid which may contain other field chemicals such as corrosion, wax, and scale inhibitors.
The present invention will also definitely affect testing and optimizing of other field chemicals (e.g. corrosion, wax and scale inhibitors). Not necessarily used in the same amount per volume unit pipe as the hydrate inhibitors, the total amount of chemicals (sometimes with environmentally highly adverse effects) are huge, as they are used in such a great number of pipelines.
The present invention provides a method for fast, systematic and effective detection and monitoring of phase transformation or solids formation such as those used for multi-testing of chemicals for controlling gas hydrates.
Many compounds, such as, for example, gas hydrates, are formed in liquids, or in mixtures of liquids and gases under elevated pressures. For testing and studying their formation, it is necessary to use pressure vessels. The pressure vessel has to be designed such that the handling of it does not represent any unnecessary hazard, provided it is used according to working instructions.
Pressure cells used for testing of gas hydrate formation are described in E. D. Sloan Jr., Clathrate Hydrates of Natural Gases, Marcel Dekker, Inc., New York, 1998, pp. 292-300. A test cell (15-300 cc) usually consists of a sight glass for visual confirmation of hydrate formation and disappearance. Normally only up to 50 per cent of the cell volume is liquids, with the remainder being gas and hydrate. The cell is enclosed in a thermostated bath with thermocouples in the cell interior to measure the thermal lag between the cell and the bath. The pressure in the cell is usually measured via Bourdon tube gages or transducers. Mixing in the cell may be provided by mechanical or magnetic agitators, by rotating or rocking the cell, by bubbling gas through the liquids, or by ultrasonic agitation. Hydrate formation is normally tested in one of three modes: isothermal (constant temperature), isobaric (constant pressure) or isochoric (constant volume). The hydrate is observed visually or detected through measurements of temperature and pressure in the cell, gas consumption, or apparent liquid viscosity.
Common to all test cells mentioned, and for all other known methods for testing of gas hydrate formation on laboratory scale, is that each pressure vessel can only perform one test mixture at the time. When a pressure vessel weights up to 8 kg, handling more than a small number of vessels at the time is difficult. This makes each test a very resource intensive process, and there is consequently a great need for more efficiency, rationalization, downscaling and automation.
Common to all the test procedures mentioned and for all other known test procedures for the testing of gas hydrate formation on laboratory scale with the purpose of discovering new inhibitors or to optimize existing inhibitors, is that these are performed in a cumbersome and expensive manner by having to separately prepare each reaction mixture, which typically consists of 4-7 reagents, and by adding the reagents one by one. Furthermore, each reaction mixture is typically prepared in batches of 5 to 100 g and tested in expensive and heavy pressure vessels with internal volumes often in the range of 25 to 250 ml and with weights of up to 8 kg per pressure vessel, causing considerable expense due to a large consumption of often expensive reagents and due to the fact that the handling of the heavy pressure vessels often makes it difficult to handle more than one pressure vessel at the time. The combination of all these elements are, according to state of the art technology, making each inhibitor test a very resource intensive process. Consequently there is a great need for greater efficiency, rationalization, down-scaling and automation.
In recent years new, automated methods for systematic preparation of new compounds, so-called xe2x80x9ccombinational techniquesxe2x80x9d, have been developed. In WO 9512608-A1 there is, for instance, a description of an apparatus and a method for a) the synthesis of several molecules on substrates, comprising distribution of the substrates in the reaction chambers, b) combination of the first addition of these molecules with different reagents in each of the reaction chambers, c) moving the substrates through tubing to separate mixing chambers where the substrates are mixed, d) redistribution of the substrates by transport through tubing back to the reaction chambers, and e) combination of a portion number two of different composition to the first portions of molecules in the different reaction chambers in order to prepare new mixtures. This publication describes only a system for mixing and distribution of different molecules and not a system for hermetical sealing the reaction chamber, which makes it possible to operate at high pressures, and this system would thus, not be suitable for testing inhibitors. In Patent Application WO 96/11878, there is a description of extensive use of a combinatorial arrangement for synthesis of new materials. Even though this patent application gives a detailed description of instrumentation and equipment developed for different purposes, pressure vessel systems required for performing the tests under the prevailing physical conditions of elevated pressure are not described.
Pressure vessels with several chambers designed for special purposes are known. There is for instance in U.S. Pat. No. 5.505.916 a description of a metal cassette which can be opened and closed like a suitcase, and which has an interior with compartments intended for placement of the different instruments ;used by dentists, where these may be sterilized by autoclaving. Furthermore, there is a series of known equipment intended for synthesis of proteins and bio-polymers, where the design comprises sheets with a large number of chambers intended for screening of synthesis and crystal growth, in its simplest form, as described in U.S. Pat. No. 5,096,676. U.S. Pat. No. 5,400,741 describes a diffusion cell for growth of the largest and the most perfect crystals possible of macromolecular compounds by a technique called the xe2x80x9changing dropxe2x80x9d technique. Several patents, for example, U.S. Pat. Nos. 5.013.531, 5,531,185, 5,362,325 and EP 0.553.539 A1, deal with cells for growth of proteins and bio-polymer crystals in spaceships. Common to the latter patents is that the designs described are very sophisticated and thus very expensive, because they are intended for use in space-vehicles. Common to all equipment designed for test and crystal growth of proteins and bio-polymers is that they are all meant for use at ambient pressures, and that they consequently are not designed to withstand conditions typical for gas hydrate formation. Typical pressures in pipelines are 40-400 bar, but for reservoirs, the pressure may range up to 1000 bar. There is, for example, a design called xe2x80x9cmultiblockxe2x80x9d (Krchnak, V., Vagner, J.; Peptide Res. 3, 182 (1990)) consisting of i) a Teflon block holding 42 reactors, polypropylene syringes equipped with polymer filters, ii) a vacuum adapter connecting each reactor to a vacuum line which enables rapid washing in a not further described apparatus for continuous flow, iii) two Teflon plates with 42 stoppers to which the Teflon block is fastened during use, and iv) a glass cover used during homogenization. The problem with this design is that the reactors, which are made of glass and which do not have protected side walls, may be used only at low pressures.
Large pressure vessels intended, for instance, for the growth of crystals, are known, and examples are described in U.S. Pat. Nos. 5,322,591 and 5,476,635. The purpose of these pressure vessels and similar ones is to make it possible to carry out large-scale synthesis, for which there is a great need in many situations, when a synthesis procedure has been established and scale-up is desired, or when the purpose is to grow single crystals as large as possible.
The only equipment known that can, in part, be used for testing of liquids and gases and mixtures thereof at elevated pressures is described in PCT/NO98/00051, wherein a xe2x80x9cmultiautoclave for combinatorial synthesis of zeolites and other materialsxe2x80x9d is disclosed. This multiautoclave has a multitude of chambers where liquids can be introduced, whereafter the chambers are sealed and this equipment might, thus, be used for practical work with combinational testing of inhibitors, in as much as zeolite synthesis requires hydrothermal treatment of a solution or gel with relatively high content of water and often high contents of organic compounds in a closed chamber. With special techniques, gases can also be introduced into the chambers of the multiautoclave disclosed in PCT/N098/00051, but this would require additional equipment not disclosed in the application unless the atmospheric pressure is sufficient. This multiautoclave also has no means for monitoring or detecting the formation of solid phases in the chambers in situ, under elevated pressure.
An important feature when dealing with a large series of tests is how gas hydrate formation, or more generally, formation of solid phases can be detected or monitored in a rational way in a multitude of test-cells in situ, under pressure, preferably in parallel, without insuperable expense, something which is not described in state of the art technology. As far as is known, this type of work is performed in the same manner by all laboratories engaged in testing of gas hydrate formation and inhibitors for gas hydrate formation.
One of the main goals of the present invention is to develop a complete system for detection of phase transformation or particularly solid structure formation in hydrocarbon systems such as those used for screening of gas hydrate inhibitors. This includes the study of conditions for formation of gas hydrates and other compounds formed in hydrocarbons and in mixtures of hydrocarbons and water under elevated pressure in a more cost efficient manner.
It is therefore important to improve a series of cost efficient parameters, such as:
1. Measuring time: the time required for testing and analyzing a certain number of experiments can be considerably reduced using a multi-test cell assembly.
2. Measuring equipment: automated measuring equipment for detection of the changes in each individual test cell in situ.
3. Data sampling: automated data sampling and storage of the detected signals from individual test cells.
4. Data treatment: automated detection and identification of formed solid structures, i.e. based on detected signals from individual test cells, a reference library stored in a database and software that can handle the sampled data and monitor the solid phase formation.
5. Dosing of reagents: a large number of test cells present in one pressure vessel can be connected to an automatic dosing set-up which makes quick and exact additions of all liquids or liquid mixtures, and an analogous system for the dosing of gases, if needed.
6. Operation: simple, fast and easy-to-use mechanism for the closing and opening of the pressure vessel and the individual test cells, including simple cleaning of the individual test cells and the pressure vessel for reuse.
Furthermore, the aim of the invention described here is to design automated equipment for larger test series and for the preparation of formulations based on mixtures of different liquids/solutions and gases with varying ratios.
These and other aims are achieved through the present invention, which represents a break-through in cost reduction for detection and monitoring of, for example, gas hydrate formation.
In accordance with the object of the invention, there is provided a multi-test assembly for evaluating, detecting and monitoring processes at an elevated pressure, comprising a pressure vessel, means for controlling the temperature and pressure in the pressure vessel, a plurality of test cells organized on one or several trays or plates arranged inside the pressure vessel, means for charging test samples into the test cells before pressurization, and means for detecting and monitoring the content of each individual test cell, in situ.
Preferably, the test cells are lined with a disposable insert or lining. The degree of interaction between the contents of the individual test cells and between the individual test cells and the atmosphere in the pressure vessel is also controllable. The contents of the individual test cells may, therefore, interact fully with the pressure vessel when the test cells are kept open, or there may be no interaction between the contents of the individual test cells when the test cells are kept closed.
Another essential part of the multi-test assembly is a sub-unit for detecting or monitoring the formation of gas hydrates or other phases in hydrocarbons. The changes in each individual test cell are to be automatically detected or monitored and the sampled data are to be stored in a matrix, for example, in a computer and treated separately. The system for detecting or monitoring phase transitions in the closed, pressurized cells is essential for the practical functioning of the multi-test unit. In principle, any system that in a reliable manner can yield relevant information about phase transformations or whatever other reaction or restructuring of matter taking place in the interior of the cells can be used, and for each specific target reaction or class of reactions, the most suitable and cost efficient method of detection or monitoring must be chosen.
In one preferred embodiment, the detecting and monitoring means may comprise a plurality of devices placed on any side of a test cell tray intended to monitor or interact with the contents of the individual test cells. An appropriately shaped magnetic stirrer may be arranged in each test cell for mixing the medium and removing gas-bubbles from the cell walls during operation. Detector means may be arranged outside the test cell wall for sensing the movement of a magnetic stirrer inside the test cell as a measure of the viscosity of the contents in the test cells.
The detecting and monitoring means may in yet another embodiment of the invention comprise optical fiber probes placed in each test cell.
In yet another embodiment, the detecting and monitoring means may comprise a xcex3-source arranged on one side of the test cell tray(s) and one or several detectors arranged opposite of the xcex3-source, on the other side of the tray(s).
Detecting and monitoring means may comprise one or more recording devices, such as a video camera, IR camera or optical fibers for observation of visible reactions or other events such as temperature changes, in all test cells simultaneously, and an appropriate marker may then be arranged in each individual test cell giving visible contrast to the image of the recording device. It is also possible to measure the mixture temperature in each individual cell using optical fibers.
The invention also comprises use of the multi-test assembly defined above for detecting solid structure formation or phase transformation in, for example, hydrocarbon systems or mixtures of hydrocarbon and water, and use of the mufti-test assembly, as defined above, for testing of inhibitors for solid structure formation as, for example, gas hydrate formation in hydrocarbon systems or mixtures of hydrocarbon and water.
In many situations, an optical method, such as optical fiber sensors, would be a suitable detection method, for instance, whenever the reaction that takes place in the cell in some way affects the transmission, reflection or dispersion of light or any particular wavelength of light. In a similar manner, other classes of electromagnetic-, X-rays or xcex3-radiation can be used to detect the phase transformations or reactions. If only one open multi-cell tray is used, one or more video or IR cameras inside or outside of the pressure vessel may be used.
If the phase transformation or the reaction in the cell leads to a change in viscosity, this can be detected by any mechanical device suitable for measuring viscosity directly, for example, by a moving magnetic body inside the cell and a sensing device outside the cell that can sense the movement of the inner body using induced currents in an electrical circuit. If the phase transformation or the reaction taking place in the cell is exothermal or endothermal, the temperature change in the cell wall can easily be monitored, for example, a thermocouple can even be mounted so that it protrudes within the wall so that the temperature in the cell content is monitored directly. Likewise, if the reaction leads to a change in pressure, this can be monitored either by a pressure transducer or other pressure sensor device in the cell or by the in-fluix or out-flux of matter, in the case the cell is connected to a reservoir at constant pressure. If the phase transformation or the reaction taking place in the cell leads to a change that affects the propagation of sound in the cell, an acoustic detecting system can be applied. Furthermore, if the phase transformation or the reaction taking place in the cell affects the conductivity of the content, this can easily be monitored, and likewise, sensors that are sensitive to certain ions or gases can be used, such as pH-electrodes or oxygen sensing electrodes in cases when a phase transformation or a reaction leads to a change in pH or oxygen activity in the cell.
In the specific case of gas hydrate formation in mixtures of hydrocarbons and water, many of the above detection systems can be applied, since the phase transformations or the reactions that lead to the formation of gas hydrates affect most of the above mentioned detectable properties of matter. Gas hydrates are white or opaque, whereas gases, water and light hydrocarbon liquids are to a certain degree transparent to light and have different light reflection properties. Thus, any of the above-mentioned optical methods of detection or monitoring can be applied. The formation of gas hydrates is exothermal, and it represents a condensation of matter, since a gaseous component is solidified, so both methods that monitor heat fluxes and pressure changes can be applied. Gas hydrate formation also affects viscosity, so any applicable method for the monitoring of viscosity can, in principle, be applied. Whenever the water-phase consists of salt water, the occlusion of the water in the solid gas hydrates will lead to changes in conductivity. Finally, since gas hydrates are crystalline compounds, they can be detected and monitored by X-ray or gamma-ray-diffraction, provided the cell-design is such that the X-rays or gamma-rays can penetrate the cell walls without loosing too much intensity. In conclusion, since a multitude of methods of detection and monitoring are available, the problem reduces to designing the cells, the pressure vessel and the other accessories in such a way that the experiments can be performed at a lowest possible cost per experiment.
The most important feature of the present invention is the fast and simple operation of the multi-test cells enabling many tests to be conducted at relatively short time, for example, having 10-1000 or more available test cells on one tray, and placing several such trays on top of each other. Automated addition of the ingredients enables quick and exact addition of all liquid or liquid mixtures. In such a system, the mixture of ingredients are brought to react in a volume reduced typically to 1/100 of what is usually used, and thereby achieving a more compact system with reduced consumption of reactants and cheaper tests.
With the present invention it is possible to change the experimental conditions such as pressure, temperature or gas mixture during the experiments, in such a way that:
all experiments are carried out at the same time by having many parallel and relatively small test cells on one or several trays/plates inside the pressure vessel,
same gas mixture feeding under the experiments, and
same temperature during the experiments.
Applications for the present invention are, in addition to gas hydrate inhibitor testing and other problems related to the production, transportation and storing of hydrocarbons, in any field of activities within research and development and routine testing related to products where at least one production-step comprises the mixing of different liquids, for example, in the fields of organic and inorganic synthesis, paint formulation, emulsions, blending of fuels, food industry, fragrants and flavors, dispersions of powders in liquid or gas, etc. Furthermore, applications within clinical testing, etc., where a liquid or gas is added to a liquid, whenever the aim is to detect/monitor or test for the formation or precipitation of solid phases, crystalline or non-crystalline. The invention is, in particular, aimed at applications where open vessels cannot be used, and more specifically for applications where it is required to operate at elevated pressures. By elevated pressure is meant pressures above 1 bar or above ambient pressure in general. For production of hydrocarbons, pressure regions of interest may typically be in the order of, but not limited to, 50 to 400 bar in production and transportation (pipeline) systems (in some cases the pressure may be higher) and 100 to 1000 bar in hydrocarbon reservoir systems. In hydrocarbon systems, the temperature will typically range from xe2x88x9250xc2x0 C. to 300xc2x0 C., but when simulating reservoir conditions the temperature may range from xe2x88x92100xc2x0 C. to 1000xc2x0 C.
Crystallization of metals and oxides and other compounds from melts have many important industrial applications. The present equipment can be designed so that it can be used for tough conditions of up to about 1000xc2x0 C., and for pressures of up to at least 200 bars.